Liquid nitrogen

Liquid nitrogen is nitrogen in a liquid state at an extremely low temperature. It is a colorless clear liquid with a boiling point of −195.79 °C. The low temperature means a risk for cryogenic burns or injury. The gas may displace oxygen and cause rapid suffocation. There is also a risk of vessels being over pressurized and cause explosion.

Liquid nitrogen may only be handled and used by people with sufficient understanding of the risks involved and safety instructions must be followed. See more information at Campus Management (also available where you collect the liquid nitrogen).

You must be shown the routines by an experienced user before you start working with liquid nitrogen.

Risk assessment

You must do a risk assessment before you start using liquid nitrogen. In here you should include specific details about how you will handle it from collecting it at Campus Management, transport to the lab and how you intend to use it.

Common risks

  • Cryogenic burns/frostbite.
  • Moist skin can freeze and adhere to metal objects that have been cooled with liquid nitrogen, which can lead to tearing and other skin injury.
  • Materials (for instance plastics) that are not designed for use at low temperature may become brittle and fracture easily.
  • There is a risk of asphyxiation when liquid nitrogen evaporates and displaces the oxygen in the air. This is especially the case in smaller enclosed spaces such as elevators or cars.
  • Accumulation of gas causes extremely high pressure and tubes, tanks and other containers must therefore never be sealed due to the risk of explosion. This applies to small volumes as well. If a container cannot be opened and safety vent is not working, and the gas has no means of escape, the SOS Alarm (112) must be contacted immediately. Evacuate the area.

Safety procedures

  • Never handle liquid nitrogen alone. Make sure someone can help you in case of an accident.
  • When transporting, pouring and handling liquid nitrogen, you must wear full face visors as well as cold insulating gloves and lab coat. Never wear open shoes (sandals) nor boots with the legs of the trousers tucked in.
  • Always use a special thermos/container intended for liquid nitrogen (for instance Dewar flasks). The use of any other container is strictly forbidden. Make sure the container is never closed with a tight lid or has a functioning safety vent.
  • When pouring the liquid nitrogen from the big reservoir, place the thermos on the floor and put the funnel into it to guide the liquid nitrogen into the thermos. Stand to the side (to keep away from the area where the nitrogen will be poured), unlock the pin to the reservoir and use both hands to guide the flow into the thermos. No one should be close to the area of the thermos, in case of a spill. When done, lock the pin and put the lid back on.
  • Keep protective equipment on while transporting the liquid nitrogen back to the lab, and when working with it in the lab. Your own lab should have this available for you to use. Be aware of your surroundings when transporting, to avoid bumping into someone.
  • Do not use the elevator if stairs can be used in a safe way. When transporting the thermos through the corridor/stairs, walk carefully to avoid stumbling and be aware of your surroundings to avoid bumping into people.
  • If an elevator is used for transport, no person is allowed to ride in the elevator with the liquid nitrogen. Place the container in the elevator, press the button “dangerous goods” and then meet the elevator at the floor it was sent to.
    Example: In an elevator of dimensions 2x2x2 m3 (8m3), a spill of 0.35 liters of liquid nitrogen is sufficient to reduce the oxygen content in the air to at a dangerously low level at under 18%.
  • Use only in well ventilated areas.
  • Note that liquid nitrogen goes downwards in case of a spill. Make sure the thermos cannot tilt over and for some purposes it might be safer to keep the thermos standing on the floor to avoid getting a spill onto your lap if working on a bench. You have to include these details in your risk assessment and take measures to minimize the risks.
  • Transport inside a car is strictly forbidden.

First aid

  • High levels of nitrogen in the air can cause asphyxiation, which can occur without warning. Symptoms may also include unconsciousness. In case of respiratory problems, the injured person must be moved away to a safe distance from the gaseous nitrogen source. Keep the person still and warm. Call for an ambulance.
  • Cryogenic injuries/cold burns are to be warmed up slowly by lukewarm water until sensation and normal colour return to the skin. Injuries must not be rubbed or handled in any other way as it could make the injury more severe. A doctor must be called if the injury is more severe. The thawing process must not be interrupted during the transport to hospital.
  • In case of splashes in the eye, the eye is to be rinsed immediately and thoroughly with water for at least 10 minutes. Always get medical attention.
  • In the event of a small spill, the room is to be evacuated while you assess the measures needed. The measures to be taken depend on the space, nature of work and air exchange. In the event of a major spill, the area is to be sealed off and properly ventilated. Cleaning up a spill is performed by ventilation. Avoid spill to the drainage system. Smaller volumes can be left to evaporate in a fume hood.
  • If a container cannot be opened and safety vent is not working, and the gas has no means of escape, the SOS Alarm (112) must be contacted immediately. Evacuate the area.

Waste

You must never pour liquid nitrogen down the drain/into the sewage system (can cause fracturing). Smaller vessels are to be placed in a ventilation fume hood where the nitrogen can evaporate safely. Make sure you leave a note, letting people know what there is liquid nitrogen in the fume hood.

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